Modern automotive transmissions typically require precise electro-hydraulic solenoid valves in order to regulate the hydraulic pressure within the various clutches and spool valves typically employed in such transmissions. The types of solenoid valves commonly employed in flow control valves used in automotive transmissions include: on/off solenoid valves, pulse-width-modulated (PWM) solenoid valves, and variable pressure solenoid (VPS) control valves. Historically automotive manufacturers have chosen to use only a single VPS control valve in their flow control valves that acts as a line-pressure regulation valve. However, in an effort to simplify the calibration of the transmissions and improve the shift quality, automotive manufacturers are now choosing to incorporate the use of several VPS control valves; electing to use them not only for line pressure regulation but also for clutch pressurization and de-pressurization.
Conventional VPS control valves provide a low control pressure by bleeding-off control pressure to an exhaust downstream from a very small upstream orifice. This method suffers from a number of problems. The first problem is excessive leakage. When only a single 2-port bleeding-off style VPS control valve is used in a transmission, the transmission fluid pump is capable of maintaining pressure even with this leakage; however, when several of these VPS control valves are used in a single transmission, the pump is no longer capable of making-up for the leakage. The second problem that is present in the current 2-port bleeding-off style VPS control valves is that the valves are not capable of reducing control pressure to zero in a normally-high pressure configuration.
The present invention is directed to overcoming one or more of the limitations of existing variable pressure solenoid control valves.